CAREER: Spatiotemporal Behavior of Stimuli- Responsive Soft Materials in Non-Equilibrium Processes

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This Faculty Early Career Development (CAREER) grant will investigate the non-equilibrium kinetic processes of stimuli-responsive soft materials (SSMs). SSMs can change their structures, shapes or functions in response to external stimuli, such as heat, chemicals, light radiation, electrical fields, or magnetic fields. Triggered by an external stimulus, a SSM evolves from one equilibrium state to a new one through non-equilibrium kinetic processes, including diffusion, reaction, viscoelastic relaxation, etc. The kinetic processes not only determine the response speeds of SSMs, but also govern how they spatiotemporally evolve their structures, shapes and functions. Understanding the response kinetics is a key step to designing programmable SSMs, and developing emerging techniques, such as 4D printing, self-folding origami, and self-propelled robots. By unraveling the coupled kinetic processes, and the interplay of kinetics with inertia and gravity, this grant will achieve programmable reconfiguration, oscillation and locomotion of SSMs. This grant has broader impacts in education and technology. It will provide training opportunities to a diverse group of undergraduate and graduate students through teaching, researching and advising. The research work will be included into graduate classes, developed into demonstrations for K-12 outreach activities, and widely disseminated in conferences. The long-term deliverables of this grant are SSMs with programmed and dynamic stimuli-responses, which will have impacts on soft robotics, biomedical devices, energy harvesting, and reconfigurable structures.The objective of this grant is unraveling coupled non-equilibrium kinetic processes and the interplay of kinetics with inertia and gravity in SSMs to control their spatiotemporal responses. Specifically, the grant will (1) unravel coupled non-equilibrium processes to achieve programmable reconfiguration, (2) utilize coupling of kinetics and inertia to enable autonomous oscillation, and (3) harness interplay between kinetics and gravity to attain controlled locomotion. Three model SSM systems, including photo-thermally responsive shape memory polymers, photo-thermally responsive hydrogels, and humidity-responsive polymers, will be analytically modeled by a nonlinear non-equilibrium field theory, computationally simulated, and experimentally fabricated and characterized. The success of the grant will advance the field of multiphysics constitutive modeling on predicting spatiotemporal behavior of SSMs, and provide design guidelines for SSMs to achieve programmable spatiotemporal reconfiguration, and fast and dynamic motion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.